The total mass of the atmosphere is about 5.3× 10 15t, accounting for 50% in the height range of 5.5km. The higher the atmosphere, the smaller the density, which means it is difficult to completely separate the atmosphere from interstellar space with an "interface". According to the differences of physical properties such as temperature, composition and charge in vertical direction and the characteristics of vertical movement, the atmosphere is divided into troposphere, stratosphere, mesosphere, warm layer and escape layer, as shown in Figure 2.3. 1.
Fig. 2.3. 1 vertical structure of the atmosphere schematic diagram
Troposphere +0
The troposphere is a layer near the ground, with an average thickness of 12 km, near the equator of 17 ~ 18 km, an average mid-latitude of 10 ~ 12 km and a high latitude of 8 ~ 9 km. The tropopause is higher in summer than in winter. Due to the gravity of the earth, this layer concentrates 75% of the atmospheric mass and almost all the water vapor. The main weather phenomena here are clouds, fog, rain, snow, cold wave, typhoon, lightning and so on. Pollution gases and sandstorms emitted by industrial and agricultural production are also mainly concentrated in this layer, which is the place where human beings and all living things depend on. The main features of the troposphere are as follows.
(1) The temperature decreases with the increase of height.
Because the atmosphere can't absorb solar short-wave radiation, but the ground can absorb solar radiation to heat and emit long-wave radiation, the atmosphere is mainly heated by absorbing long-wave radiation from the ground, and absorbs heat from the ground through convection and turbulence, so the closer the atmosphere is to the ground, the more heat it has, and the lower the temperature with height. It drops by about 0.65℃ per100 m.
(2) Strong vertical convection.
Due to the heat obtained from the ground, the low-level air is heated and the high-level cold air sinks, thus causing strong vertical convection. The equatorial region has high ground temperature, and vertical convection can reach a very high height, while the polar region has low ground temperature, weak vertical convection and low tropopause height.
(3) The horizontal distribution of meteorological elements such as temperature is uneven.
Because the troposphere is most affected by the ground, and the ground has differences in land and sea distribution and topographic relief. The horizontal distribution of meteorological elements such as temperature and air temperature in this layer is uneven.
Stratosphere in 2.3.2.2
The tropopause up to about 55 kilometers is the stratosphere. The pressure at the top of the stratosphere is about 100 Pa. Generally speaking, the temperature in the stratosphere increases with the height. Because of the existence of the ozone layer in the upper stratosphere (20 ~ 30 km), ozone absorbs the ultraviolet radiation of the sun and raises the atmospheric temperature. This inversion structure makes the stratosphere atmosphere stable and the convection weak. Most of the air moves horizontally, and atmospheric pollutants, such as nuclear explosion debris and volcanic ash, can stay in the stratosphere for a long time. There is almost no water vapor and dust in the stratosphere, and there are no clouds and weather phenomena in the troposphere. When the plane was flying in the stratosphere, it was clear in Wan Li despite the thunder and lightning.
2.3.2.3 intermediate layer
The top of the stratosphere to about 85 kilometers is called the mesosphere. The air pressure at the top of the middle layer is about 65438±0pa. The middle layer seldom absorbs solar heat. The bottom of this layer receives heat from the stratosphere through heat conduction, so the temperature at the bottom is relatively high. With the increase of height, the temperature drops rapidly, resulting in a rather strong vertical convection movement. Above 60 km, atmospheric molecules begin to ionize, and the bottom of the ionosphere is in the middle layer.
2.3.2.4 warm layer (thermosphere)
The atmosphere above the top of the mesosphere is called the thermosphere. The temperature of this layer increases with the increase of height. This is because atomic oxygen in the thermosphere can absorb 0. 1.7 micron of solar ultraviolet radiation and solar particle radiation. However, due to the difficulty of convection in the thermosphere, the heat of the atmosphere mainly depends on heat conduction, and due to the scarcity of molecules, the heat conductivity is very small, resulting in a huge temperature gradient and temperature difference between day and night. During the solar activity, the temperature is as high as 200 K during the day, and the solar radiation is weakened at night, and the temperature rises slowly, only 500 K at 500 km. The temperature of this layer is gradually rising, and it starts very quickly. After reaching a certain height, the temperature rises slowly and gradually becomes a constant temperature zone. The height at which the constant temperature starts is called the top of the warm layer. Warm layer air is in a highly ionized state.
2.3.2.5 escape layer (also known as diffusion layer)
Because the air above the top of the warm layer is thin, only10-10 ~10-2 at sea level, and the main components from low to high are oxygen, helium and hydrogen. The energy generated by the molecular collision between various artificial aircraft and this layer is very small, which does not affect the safety of the aircraft. The temperature here is high and rarely changes with height. Charged particles move fast, rarely collide with each other, and are less attracted by the earth's gravity, but they are constantly lost to space under the influence of solar wind and solar electromagnetic field. The upper boundary of this layer is fuzzy and unstable.